The present invention pertains generally to sensors which transduce physical stimuli to equivalent electrical signals for monitoring purposes and specifically to a sensor that is made self-contained in a diminutive package which is totally physically isolated from the remote location where the monitoring takes place.
Although sensors for transducing physical stimuli to equivalent electrical signals which are either processed right at the generation site or relayed to a remote location for processing or monitoring are commonplace, their usefulness is somewhat restricted by the constraints of the environment in which they operate. For example, the requirements of an external power supply for properly conditioning the transduced signal prior to either local processing or transmission to another location for remote processing or monitoring necessitates using electrical wires if a conventional continuous power source such as an A. C. system is to be employed or batteries which are located at the sensor site. When the sensor is used in conjunction with rotating machinery such as for monitoring machine forces, the machine movement entails commutation if electrical wires are used for supplying power to the sensor as well as carefully routing the wires so as not to interfere with the moving parts of the machine, while batteries at the sensor site may be required to be especially rugged to withstand the severe forces to which they can be subjected. A further disadvantage with batteries is that their size and periodic need for replacement or recharging may render them unsuitable when the space allotted for the sensor unit is particularly small or highly inaccessible.
When the transduced signals are to be processed or monitored at a location remote from the sensor, another problem arises in transmitting the signals thereto. When the sensor is used in conjunction with rotating machinery, the use of electrical wires for transmitting signals is just as troublesome as it would be for transmitting A. C. power; namely, it entails commutation and carefully routing the wires so that they do not interfere with any moving parts of the machine.
The foregoing problems are exemplified by continuous coal mining machines wherein the auger carrying the drilling bits which cut into the coal face is distant from the location of the machine operator, so that the machine itself and the highly polluted atmosphere inhibit the operator from visually determining when he is cutting into a coal seam and not rock. This necessitates that he depend solely on his own judgment and experience in differentiating the two, resulting in a greater degree of inefficiency and more dulled bits than necessary were he able automatically to monitor the forces exerted on the bits. Since coal is much softer than rock, the force exerted on a bit would provide the operator with an immediate indication of whether or not the auger was set at the proper height of the seam for mining, thus relieving the operator from reliance on his own intuitive senses. Although a force transducing sensor would accomplish this, all of the aforementioned problems associated with the use of sensors on machinery would be attendant thereto.
With the foregoing in mind, it is a primary object of the present invention to provide a completely self-contained sensor which requires no external power supply for transducing physical stimuli to equivalent electrical signals and transmitting them to a remote location for processing or monitoring.
It is a further object of the present invention to provide such a sensor which uses the transduced equivalent electrical signal both to power an A. C. signal source and to modulate the A. C. signal generated therefrom prior to transmitting.
It is still a further object of the present invention to provide such a sensor which transmits the transduced signal to a remote location without the use of electric wires.
The foregoing objects, as well as others, and the means by which they are achieved through the present invention may best be appreciated by referring to the Detailed Description of the Preferred Embodiment which follows hereinafter together with the appended drawings.